Buggy code:
Button okaybt = new Button ( "Okay" ) ; okaybt . setFont ( new Font ( 24 ) ) ; Button cancelbt = new Button ( "Cancel" ) ; cancelbt . setFont ( new Font ( 24 ) ) ; liveshb . getChildren ( ) . addAll ( livesText , livesCB ) ; liveshb . setAlignment ( Pos . CENTER ) ; bottomhb . getChildren ( ) . addAll ( okaybt , cancelbt ) ; bottomhb . setAlignment ( Pos . CENTER ) ; bottomhb . setSpacing ( 50 ) ; powerUpVB . getChildren ( ) . addAll ( liveshb , powerUpsText , fastSlowCB , sheildCB , multiCB , bigSmallCB , magnetCB , crazyCB , bottomhb ) ; powerUpVB . setAlignment ( Pos . CENTER ) ; powerUpVB . setSpacing ( 35 ) ; bpGOS . setCenter ( powerUpVB ) ; Scene sceneGOS = new Scene ( bpGOS , sceneWH , sceneWH ) ; BorderPane jsBP = new BorderPane ( ) ; VBox vbJS = new VBox ( ) ; HBox hbNameJS = new HBox ( ) ; HBox hbPortJS = new HBox ( ) ; HBox hbIP = new HBox ( ) ; Text nameTextJS = new Text ( "Name:<seq2seq4repair_space>" ) ; Text portTextJS = new Text ( "Port<seq2seq4repair_space>#:" ) ; Text ipText = new Text ( "IP<seq2seq4repair_space>address:" ) ; TextField nameTFJS = new TextField ( "<seq2seq4repair_space>" ) ; TextField portTFJS = new TextField ( "<seq2seq4repair_space>" ) ; TextField ipTF = new TextField ( "" ) ; String name = nameTFJS . getText ( ) ; String portS = portTFJS . getText ( ) ; int port = Integer . parseInt ( portS ) ; Button backJS = new Button ( "Back" ) ; Button joinGameJS = new Button ( "Join<seq2seq4repair_space>Game" ) ; joinGameJS . setFont ( new Font ( 24 ) ) ; joinGameJS . setMaxWidth ( 300 ) ; hbNameJS . getChildren ( ) . addAll ( nameTextJS , nameTFJS ) ; hbNameJS . setAlignment ( Pos . CENTER ) ; hbNameJS . setSpacing ( 75 ) ; hbPortJS . getChildren ( ) . addAll ( portTextJS , portTFJS ) ; hbPortJS . setAlignment ( Pos . CENTER ) ; hbPortJS . setSpacing ( 10 ) ; hbIP . getChildren ( ) . addAll ( ipText , ipTF ) ; hbIP . setAlignment ( Pos . CENTER ) ; hbIP . setSpacing ( 75 ) ; vbJS . getChildren ( ) . addAll ( hbNameJS , hbPortJS , hbIP , joinGameJS ) ; vbJS . setAlignment ( Pos . CENTER ) ; vbJS . setSpacing ( 50 ) ; jsBP . setCenter ( vbJS ) ; jsBP . setBottom ( backJS ) ; Scene jsScene = new Scene ( jsBP , sceneWH , sceneWH ) ; BorderPane readyQBP = new BorderPane ( ) ; BorderPane lowerRQBP = new BorderPane ( ) ; GameGUI . nameLRQ = new Label ( ) ; Button startRQB = new Button ( "Start" ) ; Button disconnectRQB = new Button ( "Disconnect" ) ; lowerRQBP . setRight ( startRQB ) ; lowerRQBP . setLeft ( disconnectRQB ) ; lowerRQBP . setPadding ( new Insets ( 10 ) ) ; readyQBP . setBottom ( lowerRQBP ) ; readyQBP . setRight ( GameGUI . nameLRQ ) ; Scene readyQS = new Scene ( readyQBP , sceneWH , sceneWH ) ; quitBSM . setOnMouseClicked ( ( e ) -> System . exit ( 0 ) ) ; playBSM . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; optionsBSM . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( optionsScene ) ) ; backBOS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( startMScene ) ) ; hostBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneHOS ) ) ; backBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( startMScene ) ) ; playBCS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( jsScene ) ) ; backJS . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; <START_BUG> joinGameJS . setOnMouseClicked ( ( e ) -> client ( Integer . parseInt ( portTFJS . getText ( ) ) ) , ipTF . getText ( ) , nameTFJS . getText ( ) ) ; <END_BUG> startHostingHO . setOnMouseClicked ( ( e ) -> readyScreen ( primaryStage , readyQS , nameTF . getText ( ) , Integer . parseInt ( portTFHS . getText ( ) ) ) ) ; optionsHO . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneGOS ) ) ; backHO . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; okaybt . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( sceneHOS ) ) ; disconnectRQB . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( choiceScene ) ) ; randomBHS . setOnMouseClicked ( ( e ) -> { int portGen = ( ( int ) ( ( Math . random ( ) ) * 9000 ) ) + 1000 ; String parsePortGen = Integer . toString ( portGen ) ; portTFHS . setText ( parsePortGen ) ; } ) ; GameScreen game = new GameScreen ( ) ; startRQB . setOnMouseClicked ( ( e ) -> primaryStage . setScene ( game . getGameScene ( ) ) ) ; startRQB . setOnMousePressed ( new EventHandler < MouseEvent > ( ) { public void handle ( MouseEvent me ) { game . continuousUpdate ( ) ; } } ) ; primaryStage . setScene ( startMScene ) ; primaryStage . show ( ) ; primaryStage . setResizable ( false ) ; } public void client ( int portNumber , String IP , String uName ) { } public void readyScreen ( Stage primaryStage , Scene scene , String hostName , int port ) { } public static void main ( String [ ] args ) { } }

Fix:
joinGameJS . setOnMouseClicked ( ( e ) -> client ( Integer . parseInt ( portTFJS . getText ( ) ) , ipTF . getText ( ) , nameTFJS . getText ( ) ) ) ;